Of the options I've seen, the one that appealed to me required a cell phone plan to use (which wouldn't be too bad if the customer could cheaply add another line via some sort of family plan). I forget the name, off hand.
There are a few options out there now.
This? http://www.integratedtrackers.com/GPSTrack/Spybike.jsp
There's also this but it seems kind of limited http://www.thetileapp.com/#this-is-tile
http://www.biketrak.com/
2014-08-11 08:53:00